A comparison of static bulk-channel charge-coupled device characteristics using uniform,Gaussian and measured impurity distributions

A comparison of the static characteristics of both three and two-phase bulk-channel CCDs with uniform, Gaussian and measured impurity distributions is presented. The characteristics are determined by using a simple one-dimensional model based upon the depletion approximation. It is shown that for phosphorus implantations that are subjected to high temperature oxidation/drive-in schedules, the resulting impurity distribution and BCCD characteristics are closer to those of the ideal uniform profile rather than the more commonly assumed Gaussian distribution.The analysis indicates that if a Gaussian impurity distribution is assumed significant errors in predicted BCCD characteristics result. For example, errors in excess of 20% occur in the calculation of the gate voltage required to hold the maximum signal charge for bulk-channel operation, and of 50% in the bulk-channel/interface potential. In the case of three-phase devices it is shown that approximation of the impurity distribution to a uniform profile gives sufficiently accurate results for most applications. However, for two-phase stepped oxide structures analysis indicates that optimisation of the maximum charge carrying capacity, whilst maintaining bulk-channel operation, can only be achieved if device operation is analysed using the measured impurity distribution.